Always honour the service schedules charted out in your car manual and change the filters and the fluids as often as instructed. Your engine must always stay in top, tuned condition and for this, sticking to regular maintenance schedule is advisable. This ensures admissible fuel emissions and also, a car that runs smoothly implies one that uses lesser fuel.
Cars these days warm up faster than the old ones so you needn’t waste your fuel on the conventional warming up for as much as half an hour or more. Always turn your car off at traffic stops or while waiting for people.
Your air conditioner in good condition would imply less of fuel intake. Also, well maintained and properly inflated tyres also make for less fuel intake. Reduce the weight of your car by disposing of unnecessary items for the same reason.